System and method for controlling operation of fuel cell hybrid system by switching to battery power in response to idle stop condition

Abstract

The present invention provides a hybrid fuel cell system that is configured to determine if an idle stop condition has been satisfied during a normal operation mode of the hybrid fuel cell system, cut off air supply to a fuel cell to stop power generation of the fuel cell and reduce a voltage which the fuel cell outputs in response to determining that the idle stop condition has been satisfied. The voltage of a bidirectional converter, connected between a battery and a bus terminal is reduced and the output of the fuel cell is controlled, based on a first predetermined value and maintained at that first predetermined value. Subsequently, the battery is charged via the output current of the fuel cell generated by maintaining the reduced voltage of the bidirectional converter.

What is claimed is: 
     
       1. A method for controlling the operation of a fuel cell hybrid system, the method comprising:
 determining, by a controller, whether an idle stop condition has been satisfied during a normal operation mode of the fuel cell hybrid system; 
 cutting off air supply to a fuel cell to stop the power generation of the fuel cell and reduce the voltage of the fuel cell, in response to the idle stop condition being satisfied; 
 reducing the voltage of a bidirectional converter, connected in series to a battery between the battery and the fuel cell via a bus terminal, to control the output of the battery; 
 controlling the output of the fuel cell, based on a first predetermined value and maintaining the first predetermined value; and 
 charging, forcibly, the battery via the output current of the fuel cell generated by maintaining the reduced voltage of the bidirectional converter, wherein oxygen in a cathode is exhausted and the voltage of the fuel cell becomes lower than the voltage of the bidirectional converter, 
 wherein in the normal operation mode of the fuel cell hybrid system, load-following operation control, in which the output of the fuel cell is controlled according to the load, is performed, and voltage upper limit control, in which a voltage control upper limit value of the bidirectional converter is determined and the voltage of the bidirectional converter controlled according to the load during operation is limited to the voltage control upper limit value of the bidirectional converter, is performed such that the use of a low output region of the fuel cell is limited by the voltage control upper limit value of the bidirectional converter. 
 
     
     
       2. The method of  claim 1 , wherein the bidirectional converter is a bidirectional high voltage DC-DC converter and in a state where the voltage of the fuel cell is reduced below the voltage of the bidirectional high voltage DC-DC converter and the voltage of the bus terminal by the exhaustion of oxygen in the cathode after forcibly charging the battery, an electric vehicle (EV) mode, in which a drive motor is driven only by the output of the battery, is performed, and the voltage of the bus terminal is determined by controlling the voltage of the bidirectional high voltage DC-DC converter. 
     
     
       3. The method of  claim 1 , wherein in the normal operation mode of the fuel cell hybrid system, if a vehicle load and a state of charge (SOC) of the high voltage battery satisfy a fuel cell OFF condition and, at the same time if the fuel cell state does not correspond to a predetermined idle stop prohibition condition, a determination is made that the idle stop condition is satisfied. 
     
     
       4. The method of  claim 3 , wherein if the vehicle load is smaller than a predetermined reference value and if the SOC of the high voltage battery is greater than a predetermined upper limit value, it is determined that the fuel cell OFF condition is satisfied. 
     
     
       5. The method of  claim 3 , wherein the voltage upper limit control of the bidirectional converter is cancelled if the fuel cell state corresponds to the predetermined idle stop prohibition condition. 
     
     
       6. The method of  claim 1 , further comprising:
 increasing the voltage of the bidirectional converter to a second predetermined value and maintaining the second predetermined value if a restart condition is satisfied in the idle stop mode of the fuel cell hybrid system; 
 restarting the fuel cell hybrid system by starting the air supply to the fuel cell in a state where the voltage of the bus terminal increases such that the voltage of the fuel cell increases to the second predetermined value and the current output of the fuel cell is made; and 
 canceling the maintenance of the second predetermined value of the voltage of the bidirectional converter after stabilization of the fuel cell such that the restart process is terminated and the fuel cell system enters the normal operation mode. 
 
     
     
       7. The method of  claim 6 , wherein when the air supply to the fuel cell is started in the restarting of the fuel cell system, an air blower is driven such that a predetermined amount of air is supplied to the fuel cell in addition to the amount of air calculated from the amount of current required for the fuel cell. 
     
     
       8. The method of  claim 6 , wherein if the fuel cell state corresponds to a predetermined idle stop prohibition condition and the fuel cell system is restarted, the voltage of the bidirectional converter is increased to a predetermined maximum value below the open circuit voltage and maintained at that level. 
     
     
       9. The method of  claim 3 , wherein the idle stop prohibition condition is selected from a group consisting of the fuel cell being in an emergency operating state, the temperature of a fuel cell stack being below a predetermined temperature, the pressure of an anode of the fuel cell stack being below a predetermined pressure, a failure in communication from an air blower controller and a heater is being operated. 
     
     
       10. A system for controlling the operation of a fuel cell hybrid system, the system comprising:
 a hybrid fuel cell system configured to
 determine, by a controller, if an idle stop condition has been satisfied during a normal operation mode of the hybrid fuel cell system, cut off air supply to a fuel cell to stop power generation of the fuel cell and reduce a voltage which the fuel cell outputs in response to determining that the idle stop condition has been satisfied, 
 reduce the voltage of a bidirectional converter, connected in series to a battery between the battery and the fuel cell via a bus terminal, to control the output of the battery, 
 control the output of the fuel cell, based on a first predetermined value and maintain the first predetermined value; and 
 charge the battery via the output current of the fuel cell generated by maintaining the reduced voltage of the bidirectional converter, wherein oxygen in a cathode of the fuel cell is exhausted and the voltage of the fuel cell becomes lower than the voltage of the bidirectional converter, 
 wherein in the normal operation mode of the fuel cell hybrid system, load-following operation control, in which the output of the fuel cell is controlled according to the load, is performed, and voltage upper limit control, in which a voltage control upper limit value of the bidirectional converter is determined and the voltage of the bidirectional converter controlled according to the load during operation is limited to the voltage control upper limit value of the bidirectional converter, is performed such that the use of a low output region of the fuel cell is limited by the voltage control upper limit value of the bidirectional converter.